The bobbins of the prior art made of wood, metal and plastics fail to assure the dynamic balance and resistance to the initial shocks and twisting forces imposed upon them by the yarn wound around them.
Thus the prior art failed to solve the many problems in forming a dimensionally precise bobbin of uniform thickness, correct dimensions and stability and high impact strength and at low costs. This is particularly true, when a big size bobbin having a flange of 9 inch diameter and a body part of 20 inch traverse is being employed. An extraordinary large size mold pattern is required for forming it integrally, using a split pattern.
The most advanced prior art employing plastics in component sections and joining them by frictional melting is disclosed in U.S. Pat. No. 3,501,110 and this invention is a substantial improvement thereover.